1. Field of the Invention
This invention is an improvement in the air distribution apparatus in the catalyst regenerator of a fluid catalytic cracking process. More specifically, the invention is an improvement in the nozzles which eject air from an air ring to a bed of coke deactivated catalyst. The invention is distinguished in reducing catalyst erosion in the nozzles.
2. Description of the Prior Art
The present invention is an improvement in the regeneration of catalyst used in a fluid catalytic cracking process such as the process described in U.S. Pat. No. 3,433,733. In a fluid catalytic cracking process, a hydrocarbon is contacted with a fluidized solid catalyst within a reaction zone to effect conversion of at least a portion of the hydrocarbon to cracked products. One cracked product is coke which deposits on the outer surface of the catalyst, reversibly deactivating it. Catalyst within an outer layer of coke is continuously removed from the reaction zone and stripped of light hydrocarbon. Stripped catalyst is then passed to the dense phase of the regeneration zone. In this zone, coke deactivated catalyst is contacted with an oxygen-carrying gas, typically air, to effect combustion of at least a portion of the deposited coke, thereby regenerating the catalyst.
Regenerated catalyst is continuously withdrawn from the regeneration zone and introduced to the reaction zone. To prompt an efficient regeneration, an even distribution of regeneration air is introduced into the lower portion of the dense phase of the regeneration zone. The efficiency of the regeneration process is dependent on the specific distribution of air through the spent catalyst zone. It has been found desirable to distribute the air outwardly from the air distributor at sufficient pressure differentials to cause the air to effectively distribute through the zone of spent catalyst. It has been found that the volume of air leaving the air distributor nozzles may be so unbalanced or unsteady between nozzles in the distributor at such desired pressure levels that turbulent eddies draw catalyst into the nozzles thereby effecting erosion. The basis for this theory of unsteady state air distribution among nozzles and aspiration of catalyst is the finding of eroded nozzles and also nozzles which have become plugged with catalyst. When a nozzle becomes plugged, air becomes maldistributed in the regenerator and regeneration efficiency decreases. Too, air velocity is increased through the unplugged nozzles enhancing turbulent flow and exacerbating catalyst aspiration, catalyst attrition and nozzle erosion.
There is a need in the art of fluid catalytic cracking catalyst regeneration for an air distribution apparatus which experiences reduced catalyst erosion in the nozzles. U.S. Pat. Nos. 4,223,843 and 4,443,551 are advances in the art of fluid catalytic cracking catalyst regeneration.